Fatigue Life Analysis of Welds in Conveyor Belts

Abstract

This report studies fatigue in welded steel structures of a conveyor belt using the finite element method (FEM) together with hand calculations based on nominal stress. Three methods were used to evaluate stress at critical locations, the nominal stress method, the hot-spot method, and the effective notch stress method. Detailed FEM models were created where weld geometry and critical stress concentrations were included through local mesh refinement in critical regions.

Several load systems were analysed to represent different operating conditions of the conveyor belt. Parameter studies were also performed to evaluate how variations
in weld size and structural configuration affect the fatigue life. The results show
differences between the evaluated methods. The effective notch method predicts higher local stress levels, while the hot-spot method describes structural stress concentrations and the nominal stress method mainly represents global stress effects.

The results indicate that local geometric variations and weld design have a strong
influence on fatigue performance. Increasing the weld size reduces the stress levels and improves the predicted fatigue life.

Different material models were also analysed. A bilinear isotropic hardening model was performed to capture the plastic deformation of the structure. The resulting deformed geometry was then used as the basis for a linear stress analysis. These analyses resulted in a lower predicted fatigue life compared to the analyses using only a linear elastic material model. Analyses including large rotation effects were also performed, but these did not lead to any significant differences in fatigue life.

Overall, the evaluated methods describe different stress fields in welded structures. The predicted stress levels and fatigue life depend on both the modelling approach and the weld geometry. This affects the choice of a suitable fatigue assessment method.

Popular Abstract

A single failure in an industrial conveyor belt can stop an entire production line. By understanding how tiny cracks develop in welded joints, engineers can design conveyor belt systems that last longer, require less maintenance, and reduce costly downtime.

Conveyor belts are essential in the modern food processing industry, where products are transported through processes such as freezing, cooking, and packaging. In spiral freezers, conveyor belts operate continuously under varying loads caused by belt tension, product weight, and changing operating conditions. Although these loads may appear moderate, the repeated loading cycles experienced during operation can gradually weaken the structure through a phenomenon known as fatigue.

Fatigue occurs when small cracks initiate and grow over time due to cyclic loading. In welded steel structures, these cracks often originate at welds, where stresses become concentrated. As the cracks propagate, they can eventually reach a critical size and cause structural failure, resulting in costly repairs and unplanned production interruptions.

This master’s thesis investigated the fatigue performance of conveyor belts used in industrial freezing systems manufactured by JBT Marel. Using computer simulations and analytical fatigue calculations, the study examined how stresses develop in critical welded connections and how different design choices influence the expected service life of the conveyor belt.

The results showed that weld geometry has a significant influence on fatigue resistance. Larger welds were found to reduce stress concentrations and improve the predicted fatigue life. The researchers also investigated an improved conveyor belt design that incorporates a tension link. This modification changes how forces are distributed throughout the conveyor belt structure and reduces the stresses acting on critical welds, leading to an increase in fatigue life.

Several established fatigue assessment methods were compared throughout the study. The results demonstrated that different methods can predict different fatigue lives because they focus on different aspects of the stress field. This highlights the importance of selecting an appropriate analysis method when evaluating welded structures.

The findings provide valuable insight into the fatigue behaviour of conveyor belt welds and can serve as a basis for future design improvements. By identifying critical locations and evaluating different design solutions, engineers can develop more durable and reliable conveyor belts for industrial food processing systems, reducing maintenance requirements, minimizing downtime, and improving operational efficiency.

• author: Larsson, Carl and Jonasson, Elias
• supervisor: Sebastian Thöns
• organization: Division of Structural Engineering
• alternative title: Analys av utmattningslivslängd för svetsar i transportband
• course: VBKM01 20261
• year: 2026
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• keywords: Fatigue, Welds, FEM, Finite Element Method, Nominal stress method, Hot spot stress method, effective notch stress method
• report number: TVBK 5315
• ISSN: 0349-4969
• language: English
• additional info: Examinator: Leandro Iannacone
• id: 9233433
• date added to LUP: 2026-06-08 17:29:35
• date last changed: 2026-06-12 17:12:25